1. Field of the Invention
The invention in general relates to bodily fluid analysis systems including a disposable test strip and a spectrophotometric sensing device, with particular application to on-site testing of particular analytes in blood.
2. Statement of the Problem
The level of certain analytes in blood and other body fluids is often used to diagnose disease, determine disease risk factors, monitor the course of a therapy, or determine the presence of illicit drugs. For example, analytes carried in blood have been evaluated to determine various cholesterol and triglyceride levels as a significant indicator of risk of coronary heart disease.
The blood analysis necessary to determine bodily fluid analytes, such as total cholesterol, high density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), and triglycerides, may be performed in clinical setting in a laboratory or on site using dry test strips. In the laboratory, the blood is centrifuged to separate the red blood cells from the plasma, and carefully controlled chemical tests in test tubes are performed to determine the concentration of analytes. Dry test strips utilize several membrane layers to separate red blood cells from blood plasma, react the plasma with a particular reagent or reagents, and obtain a signal indicative of the concentration of a particular analyte, which is usually a spectrophotometric signal. See, for example, U.S. Pat. No. 4,774,192 issued Sep. 27, 1988 to Terminiello et al.; U.S. Pat. No. 4,477,575 issued Oct. 16, 1984 to Peter Vogel et al.; U.S. Pat. No. 5,104,619 entitled “Disposable Diagnostic System”; U.S. Pat. No. 5,135,716 issued Aug. 4, 1992 to Tatin B. Thakore; U.S. Pat. No. 5,166,051 entitled “Membranes, Membrane Overlays, For Exclusion of Erythrocytes, And Method Of Immunoassay of Whole Blood Analytes”; U.S. Pat. No. 5,597,532 issued Jan. 28, 1997 to James Connolly; U.S. Pat. No. 6,171,849 issued Jan. 9, 2001 to Walter Rittersdorf et al.; U.S. Pat. No. 6,759,190 issued Jul. 6, 2004 to Jinn-Nan Lin et al., United States Patent Application Publication No. U.S. 2004/0126830 published Jul. 1, 2004 on an invention of Bruce Shull et al.; and United States Patent Application Publication No. U.S. 2005/0003523 published Jan. 6, 2005 on an invention of Sunil Anaokar et al.
All of the above systems depend on precipitation and/or filtration to separate the unwanted components from the analytes to be tested. For example, if HDL is the desired analyte, the other lipoproteins are reacted to for a precipitate and are filtered from the plasma using filter membranes. However, the precipitates tend to block the pores in the system and impede the flow the desired analytes also, which reduces the amount of the desired analytes that reach the reaction area, and thus reduces the accuracy of the test. The conflict between the need for good separation of unwanted components from the analytes and the accuracy problems associated with such separation has caused the accuracy of the test strip/spectrophotometric systems to plateau, and has limited the usefulness of this art. Thus, there is a need for a test strip/spectrophotometer architecture that can improve the capabilities of the dry strip technology system and that yield more accurate readings.